Charged particle beam exposure system

ABSTRACT

A charged particle beam exposure apparatus for transferring a pattern onto a surface of a target, comprising a beam generator comprising a plurality of n changed particle sources, substantially in one plane, each source adapted for generating a charged particle beam, a first aperture array, comprising a plurality of groups of apertures, each group of apertures aligned with one source, for splitting each beam up into a plurality of beamlets m, thus resulting in a total of n×m beamlets, and a deflector array, comprising a plurality of groups of deflectors, each group of deflectors aligned with one source and one group of apertures, each deflector in a group aligned with an aperture of the corresponding group, and each group of deflectors operable for asserting a collimating influence on its corresponding beam.

The present patent application is a Divisional claiming the benefit ofnon-provisional application Ser. No. 11/118,162 filed Apr. 29, 2005, nowU.S. Pat. No. 7,453,075 which application claims the priority ofProvisional Application No. 60/572,287, filed May 17, 2004.

BACKGROUND

Several kinds of charged particle beam exposure systems are known in theart. Most of these systems are provided to transfer very precisepatterns onto an exposure surface of a substrate. Since lithographyfeatures are pushed to become smaller and smaller following Moore's law,the high resolution of electron beams could be used to continue thedrive to even smaller features than today.

A conventional Gaussian charged particle beam exposure apparatus has athroughput of about 1/100 wafer/hr. However, for lithography purposes acommercially acceptable throughput of at least a few wafers/hr isnecessary. Several ideas to increase the throughput of such an apparatushave been proposed.

U.S. Pat. Nos. 5,760,410 and 6,313,476 for instance, disclose alithography system using an electron beam having a cross section, whichis modified during the transferring of a pattern to an exposure surfaceof a target. The specific cross section or shape of the beam isestablished during operation by moving the emitted beam inside anaperture by using electrostatic deflection. The selected aperturepartially blanks and thereby shapes the electron beam. The targetexposure surface moves under the beam to refresh the surface. In thisway a pattern is written. The throughput of this system is stilllimited.

In US-A1-20010028042 US-A1-20010028043 and US-A1-20010028044 an electronbeam lithography system is disclosed using a plurality of electron beamsby using a plurality of emitters or sources, each emitter provided forgenerating one electron beamlet. Each beamlet is then individuallyshaped and blanked to create a pattern on the underlying substrate. Asall these emitters have slightly different emission characteristics,homogeneity of the beamlets is a problem. This was corrected bylevelling every individual beam current to a reference current.Correction values for the mismatch are extremely difficult to calculateand it takes a significant amount of time, which reduces the throughputof the system. This especially turns problematic when using up to about13.000 beamlets.

In GB-A1-2.340.991 , a multibeam particle lithography system isdisclosed having a single source illumination system, which produces aplurality of charged particle sub-beams. The illumination system useseither a single ion source with aperture plates for splitting a beam insub-beams, or a plurality of sources each producing a beam which isfocused and projected. In general, the sources disclosed do not have asufficient brightness.

In Jpn. J. Appl. Phys. Vol. 34 (1995) 6689-6695 a multi-electron beam(‘probes’) lithography system is disclosed having a single, specificZrO/W-TFE thermal emission source with an emitter tip immersed in amagnetic field. The source has sufficient brightness, but a disadvantageof such a source is its limited total current. Furthermore, this sourceneeds a crossover. The mutual homogeneity of the ‘probes’ is not furtherdiscussed. Furthermore, the intensity of the source is a not sufficientfor about 13,000 beamlets.

In practise, many different approaches were proposed for multi-beamexposure systems. In one approach, one single source is used. The beamresulting from this source is split into many beamlets. In thisapproach, one single collimator lens is used. This approach has severaldrawbacks. For one, a large collimator lens suffers from aberrations.Furthermore, it proved difficult to obtain a single source which is atthe same time very bright and has sufficient total emission current fora large number of beamlets.

In another approach, instead of the single collimator lens, the beam ofa single source is split into a plurality of beamlets. Each beamlet isthen individually deflected in such a way that substantially parallelbeamlets are obtained. This will lead to large deflection angles forsome of the beamlets and thus very difficult engineering challenges.Furthermore, again, it proved difficult to obtain a single source whichis at the same time very bright and has sufficient total emissioncurrent for a large number of beamlets.

In yet another approach, n sources and n collimator lenses are used. Adisadvantage of this approach is that is difficult to obtain therequired number of beamlets per area of surface of the substrate: lensesfor charged particle beams usually have a diameter which is about 10times larger than the diameter of a beam. The different groups ofbeamlets will thus be spread over a large surface area.

SUMMARY OF THE INVENTION

It is an objective of the current invention to improve the performanceof known charged particle beam exposure apparatus.

Another objective is to improve the resolution of known charged particlebeam exposure apparatus.

Yet another objective of the current invention is to improve throughputof known charged particle beam exposure apparatus.

Yet another objective of the current invention is to overcome theproblems related to Coulomb interactions and the demagnification methodsin the prior art.

Another objective of the current invention is to simplify controllinguniformity of beamlets, especially during writing.

The invention relates to a charged particle beam exposure apparatus fortransferring a pattern onto a surface of a target, comprising:

-   -   a beam generator comprising a plurality of n changed particle        sources, substantially in one plane, each source adapted for        generating a charged particle beam;    -   a first aperture array, comprising a plurality of groups of        apertures, each group of apertures aligned with one source, for        splitting each beam up into a plurality of beamlets m, thus        resulting in a total of n×m beamlets, and    -   a deflector array, comprising a plurality of groups of        deflectors, each group of deflectors aligned with one source and        one group of apertures, each deflector in a group aligned with        an aperture of the corresponding group, and each group of        deflectors operable for asserting a collimating influence on its        corresponding beam.

In this way, it is possible to illuminate a large area with a sufficientbeam current in each beamlet whilst avoiding the problems relating toaberration of collimator, which amongst others relate to the nature oflenses for charged particle beams, and aberrations due to these lenses.Furthermore, it is possible to provide sufficient beamlets per area onthe surface of a target.

A large throughput can be obtained by illuminating a large area at atime by using many beamlets. In the approach of the invention,homogeneity and at the same time generating sufficient current per areaat the target is possible. Furthermore, when using several sources fortogether illuminating a large area of up to 26×26 mm, the requiredopening angle problems can be overcome.

In an embodiment, in each charged particle beam has a beam axis and eachgroup of deflectors has a centre which is aligned with a beam axis. In afurther embodiment, each deflector of a group of deflectors is operablefor deflecting charged particles towards the centre of the group ofdeflectors. In yet a further embodiment thereof, each deflector in agroup of deflectors is adapted for asserting a force on chargedparticles which is equivalent to its distance from the centre of thegroup.

In another embodiment, said first aperture array is located before saiddeflector array.

In another embodiment, the apparatus of the invention further comprisesa second aperture array, comprising a plurality of groups of apertures,each group of apertures aligned with a group of deflectors and eachaperture aligned with a deflector, and said second aperture arraylocated after said deflector array, wherein preferably the area of eachof the second apertures is smaller than the area of the first apertures.

In another embodiment of the invention in the apparatus of the inventionthe inter-beamlet distance, being the distance between beamlets of agroup, is about equal to the inter-group distance, being the distancebetween the nearest beams of neighbour groups.

In an embodiment thereof, an apparatus with beamlets which have adiameter at the surface of a substrate which is smaller than about 100nm, in practice even smaller than 20 nm, the inter-beamlet distance willbe about 100-200 micron. In such an embodiment, the distance betweensources of a beam generator will be about 1-2 mm.

In another embodiment, the apparatus further comprises a lens arraycomprising a plurality of groups of lenses, each group of lenses alignedwith a group of deflectors and each lens aligned with a deflector forreceiving a beamlet, wherein each lens is operable for focussing abeamlet to a cross section smaller than 100 nm on the surface of thetarget.

Many of the features described in this document may be combined.

In another embodiment, the charged particle source is an electronsource, such as a schottky emitter. In an embodiment thereof, saidsource comprises an array of tips coated with work-function-loweringmaterial, and at least one heater for heating said tips. In anembodiment thereof, said source further comprises at least one reservoirfor work-function-lowering material, arranged for allowingwork-function-lowering material to diffuse from said reservoir to saidtips. These tips can be regularly arranged in said array, and said tipshave a radius of about 100-2000 nm.

The invention further pertains to an electron beam generator forgenerating a plurality of electron beams, said electron beam generatorcomprising a plurality of Schottky emitters substantially regularlyarranged in one plane, each emitter comprising a tip coated withwork-function-lowering material, at least one heater for heating saidemitters, and at least one reservoir for work-function-loweringmaterial, arranged for allowing work-function-lowering material todiffuse from said reservoir to said tips.

In particular, each emitter can be composed as described inPCT/NL2004/00112 of the same applicant, which document is enclosedherewith as if fully set forth.

Such a beam generator is in particular suited for the apparatusdescribed above.

The invention further pertains to a method for transferring a patternonto a target exposure surface, using an apparatus described above, andto a wafer processed using the apparatus of the current invention. Theapparatus can furthermore be used for the production of mask, like forinstance used in state-of-the-art optical lithography systems.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be further elucidated in the following embodiments ofan electron beam exposure apparatus according to the current invention,in which:

FIG. 1 shows an apparatus according to the present invention,

FIG. 2 shows another embodiment of an apparatus according to the presentinvention,

FIG. 3 shows an electron source according to another aspect of theinvention,

FIG. 4 shows another embodiment of an electron source according toanother aspect of the invention.

DESCRIPTION OF EMBODIMENTS

An embodiment of the present invention is schematically shown in FIG. 1.Electrons are emitted from several electron sources 1. The beamgenerator of the device has sources 1, each source 1 emitting anelectron beam.

An illumination system (4, 6, 8) focuses and collimates each of theemitted electron beams 2 to illuminate a desired area on an apertureplate or aperture plates 4 uniformly.

The illumination system can be combined with all the features describedin applicants co-pending patent applications U.S. 60/453,745 of Mar. 10,2003 U.S. Ser. No. 10/600,953 of Jun. 20, 2003 U.S. Ser. No. 10/692,632of Oct. 24, 2003 U.S. 60/491,475 of Jul. 30, 2003, and U.S. 60/473,810of May 28, 2003 U.S. Ser. No. 10/699,246 of Oct. 30, 2003 or familymembers or continuations of these US patent applications, which are allincorporated by reference as if fully set forth. All the devices,combinations thereof and specific elements, in most cases described forsingle beam systems, can be used in the current system.

In the system of the current invention, in an embodiment, one aperturearray 4, one collimator 6 and one focussing lens array 8 can be used.All these devices can have their specific elements divided in groups,each group arranged to work on one beam 2.

In another embodiment, each beam can have its own set of devices (4, 6,8), and these devices can be aligned with its proper beam in order tooptimise performance.

In FIG. 1, each emitter or emitting source 1 produces a diverging beam 2with an optical axis 3. In the embodiment of FIG. 1, each beam has thefollowing optical system, which is, as explained above, one example of apossible (charged particle) optical system.

In the optical system of FIG. 1, each beam is provided with a group ofbeam splitters 4, for providing a group of beamlets 5. Each group ofbeamlets is provided with a collimator 6. In an embodiment, thecollimator comprises a group of deflectors. The group of deflectorstogether have a collimating influence on the group of beamlets 5. Themeans that after the collimator, the optical axes of the beamlets 7 aresubstantially parallel.

After the collimator, the apparatus is provided with groups of lensarrays 8 one group for each group of beamlets, for focussing eachbeamlet to a cross section smaller than 100 nm on the substrate 10. InFIG. 1, the inter-beamlet distance is indicated with d1, and theinter-group distance is indicated with d2. In a preferred embodiment, d2is about the same as d1. In an embodiment of the invention, the beamletsin a group are arranged in a hexagonal arrangement. These hexagonalgroups can easily be stitched together in a close packing.

The system of FIG. 1 further has an extraction electrode 102 for eachsource. Each extraction electrode is operated by an operator 100. Thesystem further has a controller 101 for controlling the operators 100 insuch a way that the intensity and current density of each source 1 iscontrolled. The system may further be provided with measuring devices(not shown) for measuring the intensity and/or current density of eachsource 1. The measuring devices provide input to the controller 101.

In FIG. 2 another embodiment of the system of the invention is shown. Inthis embodiment, beam splitter groups 4, collimator groups 6 and lensarray groups 6 are each attached to one another. In an embodiment thesedevices are each provided on a single plate. In a further embodiment,these plates can be integrated by for instance attaching these plates toone another. These plates can for instance be produced from a (silicon)wafer which is etched and processed using well-know techniques andprocedures.

In the present invention, a combination of sources, thus providing asource as shown in FIGS. 3 and 4, may be used. Preferably, an array ofseparate Schottky emitters is used, as indicated in FIGS. 1 and 2.

In an embodiment shown in FIG. 3, the electron source has varioussources 13 on one single substrate 12. The sources typically deliver1000 A/cm² from an area of about 0.1-2 micron squared. In an embodiment,thermionic sources are used. The electrons are preferably emitted in thespace charge limited emission regime in order to benefit from ahomogenizing effect of the space charge. Examples of such a source are aLaB₆ crystal, a dispenser source comprising Barium Oxide, or a dispensersource comprising a layer of Barium or Tungsten covered with a mixturecomprising Scandium Oxide or a source comprising crystalline tungsten 12with areas of zirconium oxide 13, acting as sources.

In a preferred embodiment, shown in FIG. 4, a dispenser source is usedcomprising for instance a Tungsten substrate 12 with crystallinetungsten tips 1 as sources, regularly spaced, covered with a layer 13 ofZirconium Oxide of a functionally similar substance. The beam generator11 furthermore comprises a reservoir 14 of this material. In anotherembodiment a LaB₆ substrate 12 with crystalline LaB₆ tips 1 as sources,regularly spaced, is used.

In another embodiment, several of the sources described inPCT/NL2004/00112 are regularly spaced in an array in order to providethe sources of the current invention.

It is to be understood that the above description is included toillustrate the operation of the preferred embodiments and is not meantto limit the scope of the invention. From the above discussion, manyvariations will be apparent to one skilled in the art that would yet beencompassed by the spirit and scope of the present invention.

1. A method for transferring a pattern onto a target exposure surfacecomprising: generating a plurality of n charged particle beams (3)utilizing a beam generator, wherein each charged particle beam (3) has abeam axis (2); splitting each beam (3) of said n charged particle beamsinto a plurality of m beamlets (5), thus resulting in a total of n×mbeamlets (5), said splitting being accomplished by a first aperturearray (4), comprising a plurality of groups of apertures, each group ofapertures aligned with one of said n charged particle beams (3); anddeflecting said m beamlets (5) of each beam (3) utilising a deflectorarray comprising a plurality of groups of deflectors, each group ofdeflectors has a centre which is aligned with the beam axis (2) of onebeam (3) of said n charged particle beams, wherein each deflector of agroup of deflectors is operable for deflecting charged particles towardsthe centre of the group of deflectors.
 2. The method according to claim1, wherein each group of deflectors is aligned with one beam (3) and onegroup of apertures, each deflector in a group is aligned with anaperture of the corresponding group.
 3. The method according to claim 2,wherein each deflector in a group of deflectors is operable forasserting a force on charged particles which is equivalent to itsdistance from the centre of the group.
 4. The method according to claim1, wherein said first aperture array is located before said deflectorarray.
 5. The method according to claim 1, wherein said deflectors areoperable for directing said beamlets towards an aperture of a secondaperture array or not, comprising a plurality of groups of apertures,each group of apertures aligned with a group of deflectors and eachaperture aligned with a deflector, and said second aperture arraylocated after said deflector array.
 6. The method according to claim 1,wherein each beamlet (5) is focussed to a cross section smaller than 100nm on the surface of the target utilising a lens array comprising aplurality of groups of lenses, each group of lenses aligned with a groupof deflectors and each lens aligned with a deflector for receiving abeamlet.
 7. The method according to claim 1, wherein the beam generatorcomprises a plurality of n charged particle sources (1), substantiallyin one plane, wherein each source (1) is utilised for generating onebeam (3) of said n charged particle beams.
 8. The method according toclaim 7, wherein the charged particle source (1) is an electron source.9. The method of claim 1, utilising a first aperture array situated on asingle substrate.
 10. The method of claim 1, utilising a deflector arraysituated on one single substrate.
 11. The method of claim 1, utilising adeflector array and an aperture array situated on one single substrate.